The present invention relates in general to an electric arc vapor deposition device for depositing coatings on various types of articles.
Electric arc vapor deposition devices employ a high current electric arc to evaporate material off of a cathode and form a vapor, which is then deposited on articles to be coated. Examples of these types of devices are disclosed in Sablev U.S. Pat. Nos. 3,783,231 and 3,793,179 and Mularie U.S. Pat. No. 4,430,184. In the devices set forth in these patents, a power supply is used to strike and sustain an arc between an anode and a planar metal cathode disposed in an evacuated chamber. As the arc travels along the cathode, the cathode metal, such as titanium, is vaporized, reacted with nitrogen and used to coat articles in the chamber, such as gears, cutting tools and machine parts. A problem with these types of devices is that the arc wanders erratically across the face of the cathode and causes an uneven consumption of the cathode material which reduces its life expectancy. In addition, a means must be provided to prevent the arc from wandering off of the cathode face and extinguishing or evaporating non-cathode material within the chamber.
In the Sablev et al. patents, a magnetic field is employed to help confine the arc so that the cathode is evenly eroded, and an anode referenced annulus is provided to extinguish the arc if it travels off of the cathode face. This leads to erratic operation of the source and requires numerous restrikings of the arc which generate very large particle emissions that, if included with the vaporized coating material, can cause a rough coating. The anode ring also requires maintenance because coating material quickly builds up on it which must be stripped periodically to prevent electrical short circuits.
In the device disclosed in the Mularie patent, an active boron nitride confinement ring is utilized to keep the arc on the cathode face. This boron nitride ring must be in intimate contact with the cathode or the arc will migrate into the interface between the two and extinguish. When fitted properly, the boron nitride ring allows the arc to continue operating by bouncing it back onto the cathode. A problem with this arrangement is that much larger particulate material is produced when the arc continues to operate on or near the boron nitride. This, combined with the higher amperages needed to maintain its operation, can lead to rough, contaminated thin film coatings.
In view of the foregoing, an electric arc vapor deposition device is needed which employs an improved arc confinement technique that does not suffer from the drawbacks of the prior art devices and provides a more uniform utilization of the cathode material to improve coating quality and extend the life of the cathode.